Human lymphocytes have insulin receptors on their cell surface. In the proposed project, the radiolabeled lymphocyte insulin receptor will be obtained from cultured human lymphocytes by gentle agitation and purified by chromatographic procedures, including affinity chromatography. The receptor will also be characterized with respect to its binding properties, including specificity, stoichiometry, affinity, cooperativity, and thermodynamics (equilibrium and kinetic). The receptor preparation will be characterized with respect to its physical properties, including homogeneity, molecular weight, axial ratio, density and subunit structure. Insulin-receptor interactions will be studied by examining the receptor for insulin-induced changes in sedimentation or electrophoretic behavior, circular dichroism, or protein fluorescence. The presence of these changes may demonstrate the presence of insulin-induced conformational changes. Attempts to reassemble the receptor with the cellular effector systems of the lymphocyte and adipocyte will be undertaken. This will be monitored by cellular uptake of the radiolabeled receptor, increased cellular I 125-insulin binding, and a stimulation of an insulin-induced biological response. The above characterization of the insulin receptor of the human lymphocyte will provide a basis for further investigation of the mechanism of insulin action in humans.